Performance of the new hadron blind HADES RICH in heavy ion collisions.

The High Acceptance Dielectron Spectrometer (HADES) situated at GSI Darmstadt, Germany, has recently upgraded its gaseous ring imaging Cherenkov (RICH) detector. Studying the properties of the hot and dense fireballs produced in heavy ion collisions the RICH is the key component to efficiently identify electrons and positrons emitted therein. The new photon detection plane is comprised of 428 multianode photo electron multipliers (MAPMT)(Hamamatsu H12700) partly coated with p-Terphenyl as a wavelength shifter. It is operated with a gaseous C 4 H 10 (isobutane) radiator making it essentially hadron blind for particle momenta up to approximately 2.5 GeV/c. All 27392 MAPMT channels are read out by an FPGA based readout electronic scheme called DIRICH, which will also be used in other future Cherenkov detectors. The DIRICH readout allows to measure leading and trailing edges for each pixel pulse and hence time over threshold and hit arrival time down to sub-nanosecond precision. This article will discuss the key features of the upgraded HADES RICH and its performance based on a Ag+Ag run at E = 1. 58 A GeV incident energy within the FAIR Phase-0 research program. • HADES RICH upgraded with 428 Hamamatsu H12700 MAPMTs. • 200 ps timing precision reachable using DIRICH readout chain for MAPMT readout. • More than 17 hits per ring reached on average over full detector. • Detector integrated average of less than 15 background hits per event. [ABSTRACT FROM AUTHOR]